1. Technical Field
The present invention relates to medical devices and particularly to a blood flow monitor with a visual display.
2. Background Information
The monitoring of blood flow in a vessel can be accomplished by several methods. One method uses the principle of Doppler frequency shift to measure blood flow. According to this principle, a signal reflected by a moving object will exhibit a frequency shift. The direction and degree of the frequency shift represents the direction and velocity of the moving object.
Doppler blood flow monitors typically will excite a transducer associated with a blood vessel with a short burst of ultrasonic energy. The transducer will then “listen” for a reflected signal. The difference in frequency between the original burst of energy and the reflected signal represents the velocity of the blood cells moving past the transducer. Typically, this difference is ultimately delivered to an audio speaker. By listening to the audio output of the blood flow monitor, the operator can make an assessment as to the presence of adequate blood flow in the vessel.
There are multiple shortcomings with blood flow monitors that solely have an audio output. The audio nature of the monitors limits access for persons with hearing impairments. Even for persons without a hearing impairment, every person's hearing abilities are different, particularly for low frequencies, which may make an audio output unsuitable for some persons.
Moreover, the design and manufacture of compact and portable blood flow monitors that are capable of producing very low audio frequencies is extremely difficult. In many cases, the small speakers used with portable monitors have a frequency response starting at 100 Hz, which prevents any audible indication of blood flow for low flow rates.
Additionally, the ability to detect lower velocities (and the resultant lower frequency shift) is extremely important, particularly for large blood vessels. With large vessels, the flow rate may be less to deliver the same quantity of blood compared with a smaller vessel. For example, the actual amount of blood flowing, at some given velocity, is quite different in a 1 mm vessel as compared to a 4 mm vessel.
Therefore, there is a need for a blood flow monitor that is capable of indicating a flow rate in a non-audible manner.